The present invention relates generally to fume hoods used in laboratories and the like to permit technicians to work on materials within the confines of the interior cabinet of the fume hood without exposure to toxic or otherwise dangerous fumes that may be generated by such work, and more particularly to a fume hood of this type in which the fumes or contaminated air is maintained substantially within the confines of the interior cabinet, even when access to the interior is undertaken through a sash opening, by a unique pattern of air flow within the interior of the cabinet.
Fume hoods are constructed with a wide variety of air flow arrangements for directing the flow of outside air in a desired path within the confines of the interior chamber. For example, in Bayern U.S. Pat. No. 3,237,548 a flow path is created within the confines of the fume hood that includes a directed flow of air downwardly along the plane of the sash or door of the fume hood to prevent the escape of contaminated air when the door is open.
In Turko U.S. Pat. No. 3,747,505 a diffuser is provided to direct auxiliary air directly downward and somewhat outwardly when the fume door is open to combine with outside air and form an air flow path that sweeps along the plane of the open door and then along the bottom of the interior cabinet to contain contaminated air within the cabinet. A somewhat similar air flow path is disclosed in Chamberlin U.S. Pat. No. 3,752,056 where a plenum is located above and outside of the door of the fume hood.
In McNeil U.S. Pat. No. 2,819,666 a baffle plate is provided above the door to direct auxiliary air downwardly along the interior surface of the door of the fume hood when it is in its closed position, and this air flow is cut off when the door is opened and air from an upper plenum is used to created a screen of auxiliary air generally in front of the plane of the door when the door is open. Also, a flow of outside air is introduced into the bottom of the interior cabinet of the fume hood and is directed inwardly along the bottom wall of the interior cabinet to remove heavy contaminated air within the cabinet.
A somewhat similar flow pattern is disclosed in Grow U.S. Pat. No. 4,177,718 where a valve member is moved between one position when the fume hood door is closed to direct air downwardly along the interior surface of the door, and another position when the door is open to create a flow of auxiliary air downwardly along the outside plane of the open door.
In accordance with the present invention, an apparatus and method are provided for containing and properly directing contaminated air within the confines of a fume hood or the like. The apparatus includes a housing forming a generally rectangular interior cabinet that has side walls, a back wall, a top wall, and an open front face, and a door disposed for movement between a closed position closing the open front face and an open position creating an opening through which a technicians hands can extend to work within the interior cabinet. An exhaust plenum is located within the interior cabinet adjacent the back wall thereof, and it is adapted to be connected to an exhaust source for exhausting air from within the interior cabinet. A bypass slot is formed in the housing and disposed to direct outside air downwardly generally along the inside surface of the door, and openings are formed in the door and are disposed to admit outside air into the interior cabinet in a direction generally transverse to the flow of outside along the inside surface of the door to thereby cause the combined flow of the outside air to flow in a direction generally directly toward said exhaust plenum.
In the preferred embodiment of the apparatus of the present invention, the door moves in a vertical direction between the open and closed positions thereof, and a contoured air foil is attached to the bottom edge of the door to direct a flow of outside air inwardly toward the back wall when the door is in its open position.
Additionally, it is preferred that a wall portion be disposed adjacent the upper portion of the interior cabinet and be inclined inwardly and downwardly, and that the bypass slot be formed between the lower end portion of the wall portion and the upper end portion of the door.
It is also preferred that the housing include an air exhaust opening disposed in the top wall thereof generally adjacent the back wall thereof, and in communication with the exhaust plenum.
The method of the present invention includes the steps of creating a first flow path of outside air inwardly into the interior chamber through a by-pass slot formed in the fume hood housing in a direction generally downwardly along the inside surface of the door, creating a second flow path of outside air though the door which is generally inwardly toward the back wall of the interior cabinet, and creating an area of uncontaminated air adjacent the back wall of the interior cabinet. Preferably, the method includes the step additional of creating the aforesaid region of uncontaminated air through air flow through vertical clearance slots formed between the overlapping edges of glass panels included in the door.
In the preferred embodiment of the method of the present invention, such method includes the step of positioning a wall portion within the interior cabinet so that the lower edge thereof is spaced from the door to create the first flow path of air. The method may also include the step of disposing an airfoil along the bottom edge of the door and forming the airfoil with a contour for directing the second flow of outside air inwardly toward the back wall of the interior chamber when the door is opened. Finally the method may include the step of exhausting the outside air from the interior cabinet though an opening in the top wall of the interior cabinet.